This invention relates generally to steam turbine engine components, and, more specifically, to methods and apparatus that facilitate cooling of steam turbine engine components.
At least some known combined-cycle power plants include a steam turbine that is coupled to the gas turbine with a single shaft. Such power plants may be referred to as having a single-shaft, combined-cycle configuration. During at least some operations of such a power plant, the gas turbine may carry a load while the steam turbine does not carry a load. However, during such operations, because the steam and gas turbines are coupled to the same common shaft, the steam turbine must operate at full speed without carrying a load. When the steam turbine is at full-speed, no-load operation, at least some steam turbine components may increase in temperature because of windage within the steam turbine.
To facilitate preventing wear to components, in at least some known single-shaft, combined-cycle power plants, the steam turbine is uncoupled from the gas turbine when the gas turbine is carrying a load, but steam turbine is not carrying a load. As such, the steam turbine does not operate at full-speed, no-load conditions while the gas turbine is carrying a load. However, before the steam turbine can take on a load, the steam turbine must be re-coupled to the gas turbine. As is known, synchronizing steam turbine operation with gas turbine operation during re-coupling may be a difficult and time-consuming task.
Other known single-shaft, combined-cycle power plants allow the steam turbine to operate at full-speed, no-load operation while the gas turbine is carrying load. Such plants utilize a cooling fluid, such as air or steam, to facilitate cooling the steam turbine. However, before steam can be introduced into a steam turbine, the steam must be substantially free of water droplets because such droplets may cause damage therein. To facilitate preventing water droplets from being introduced into the steam turbine, at least some known combined-cycle plants channel the steam to a superheater integral with an auxiliary boiler to superheat the steam before channeling the steam to the steam turbine. However, such superheaters are generally physically large and may be costly to purchase and/or operate because such superheaters generally require a considerable power supply to ensure all of the water within the steam is substantially vaporized.